Tumbling is a surface finishing operation in which workpieces are caused to move in a bed of treating elements, e.g. abrasive particles, or against one another in such manner that the relative motion between the workpieces and the treating elements causes an alteration of the surface, e.g. a polishing, deburring or material removal.
It has been proposed heretofore to improve upon the tumbling action of a simple rotation of the drum by providing a double rotation or two-axis tumbling action.
Such a system is described in German Patent Document No. 1,767,318. In that system a working container which can be closed and can receive the workpieces and treating elements, is rotatable about a first axis, the container being journaled for such rotation on a movable frame. The movable frame, in turn, can be rotated about a second axis which is coplanar with the first, relative to a main frame or support. Drive means are provided for rotating the drum about the two axes.
The two axes extend through the container and intersect within the container.
The drive means can be effective to hold the contents of the container against the container walls by centrifugal force, but because centrifugal forces about two axes are superimposed, relative motion between the two workpieces and the treating elements is reinforced by comparison with the action obtained when only single axis rotation was provided.
This apparatus, therefore, can allow higher angular velocities to be used and generally has been believed to bring about a more effective surface treatment than single axis tumbling.
German Patent Document No. 1,767,318, however, does not provide verifiable results along these lines, but is evidence of the fact that improvements in tumbling operations have been required in the past. Indeed, I have found that tumbling processes require further improvement and are not fully satisfactory even when carried out with rotation about two coplanar axes.